Two recent techniques are now deemed major developments in the field of producing nodular cast iron, namely; mold-modulizing and continuous stream treatment. Each of these treatments or processes can be used for purposes of treating molten metal to achieve a variety of different metallurgical changes.
This invention is particularly concerned with continuous stream treatment wherein a reaction takes place in a closed launder situated in the metal flow either between the furnace and a pouring ladle or between the ladle and the mold. In contrast, the mold nodulizing process enables nodulizing to take place within the mold by incorporating a specially designed gating system. However, mold nodulization is limited in capacity and is not particularly suitable to optimum production when dealing with pouring tonnages exceeding 1500 lbs. (maximum poured weight). For a more complete explanation of the state of the art with respect to stream treatment, reference is made to U.S. patent application Ser. No. 569,029, filed 4-17-75, commonly assigned to the assignee hereof; the disclosure of said patent application is incorporated herein by reference.
In spite of the fact that continuous stream treatment is more suitable to larger poured weights, there remains certain limitations which must be overcome, such as (a) greater reliability of treatment so that there is a uniformly high degree of nodularization throughout the entire casting, (b) the existence of dirty treating chambers having a residue resulting from practising the process sequence, (c) relatively low nodulizing agent recovery, (d) the need for a more controllable treatment process to allow for use of different casting weights without alteration of the process, (e) excess maintenance of process equipment, and (f) the need for expensive multiple core type launders or treating devices. The lack of proper homogenization may, in part, be due to inadequate mixing of the treating agent with the molten metal in a properly sequestered manner so that a greater volume of the treatable metal is contacted by such agent within a relatively short treating period. Thus, the character of the flow of the treatable metal and treating agent become of importance, as well as the character of the particle of the treating which is to be immersed in such treatable metal.